1. Field of the Invention
This invention relates to a projector provided with a plurality of image generators, and particularly to a projector provided with a plurality of image generating liquid crystal light bulbs and projecting images of different colors formed by the liquid crystal light bulbs onto a screen to thereby display a color image on the screen.
2. Related Background Art
FIG. 1 of the accompanying drawings is a cross-sectional view showing an example of a liquid crystal device according to the prior art having a scattering mode for scattering incident light. The layer 803 between a pair of transparent glass substrates 801 and 801' kept at a predetermined interval is impregnated with a high molecular medium 803a and droplets 803b comprising liquid crystal molecules having positive dielectric anisotropy dispersed in said high molecular medium 803a. Transparent electrodes 802 and 802' are disposed on the inner surfaces of the glass substrates 801 and 801'. The materials of the high molecular medium 803a and the liquid crystal molecules are chosen so that the refractive index of the former and the ordinary refractive index of the latter may be equal to each other.
When no voltage is applied between the transparent electrodes 802 and 802', the liquid crystal molecules in the droplets 803b are oriented at random and therefore, the incident light onto the liquid crystal device are scattered in the droplets 803b. On the other hand, when a voltage is applied between the transparent electrodes, the major axes of the liquid crystal molecules become uniform in a direction perpendicular to the surfaces of the glass substrates 801 and 801' and therefore, the refractive indices of the liquid crystal molecules and the high molecular medium coincide with each other. Accordingly, the incident light onto the liquid crystal device travels straight without being scattered by the droplets 803b.
As a liquid crystal device of similar scattering type, there is one of the type in which low molecular liquid crystal is dispersed at random in a network comprising high molecular mediums overlapped with each other.
These liquid crystal devices of the scattering type, unlike TN liquid crystal devices, for example, do not require any polarizing plate, and this leads to the advantage that they have a high rate of light utilization and are easy to obtain a bright image when they are used as a display device.
FIG. 2 of the accompanying drawings is an illustration showing one of constructions conceivable when the liquid crystal device of the above-described scattering type is applied to a color projection type display apparatus.
A white light beam emitted from a light source 701 comprising a halogen lamp, a xenon lamp or the like enters a condensor lens 703 directly or through a reflector 702 and is made into a parallel light beam by the condensor lens 703. The parallel light beam is resolved into light beams of three colors by a color resolving system comprising a dichroic mirror 704 for reflecting blue, a dichroic mirror 705 for reflecting green and a total reflection mirror 706, and the respective light beams enter liquid crystal devices 710R, 710G and 710B. Each of the liquid crystal devices 710R, 710G and 710B is divided into a plurality of matrix-like picture elements, each of which is independently driven by an electrical signal conforming to the substance of display and becomes scattered or transparent relative to the incident light beam. The light beams transmitted through the liquid crystal devices 710R, 710G and 710B are again made into a light beam having the information of color images by a color combining system comprising a dichroic mirror 707 for reflecting green, a dichroic mirror 708 for reflecting red and a total reflection mirror 709. Thereafter, the light beam passes through a condensing lens 711 to a light intercepting plate 712 having an aperture which defines an opening about the optical axis. With regard to the light which enters each picture element of the liquid crystal devices 710R, 710G and 710B, the light beam passing through the picture element which is in a transparent state passes through the aperture portion of the light intercepting plate 712 and is projected onto a screen, not shown, by a projection lens 713. On the other hand, the light beam passed through the picture element which is in a scattered state is intercepted by the light intercepting portion of the light intercepting plate 712 and does not arrive at the projection lens 713 and therefore, is not projected onto the screen, not shown. By the scattering-transmitting mode of each picture element of the liquid crystal devices 710R, 710G and 710B being thus changed over, image display can be accomplished.
However, of the light beam scattered by the picture element which is in a scattered state, rays of great scattering angle, like the rays .alpha..sub.2 and .beta..sub.2 of FIG. 2, re-enter other adjacent liquid crystal device 710G (the ray .alpha..sub.2) and re-enter the same liquid crystal device 710G (the ray .beta..sub.2) before they are processed by the light intercepting plate 712. Part of such rays is scattered by the liquid crystal device 710G which they have re-entered, and passes through the aperture portion of the light intercepting plate 712 and is displayed as ghost or flare on the screen, thereby deteriorating the quality of image on the screen.
A similar situation occurs not only in the liquid crystal device of the aforedescribed scattering type, but also in all of light bulbs using a mode in which light is diffracted or refracted and the direction of travel of this light is changed, such as those which use liquid crystal to form a diffraction grating.